Looking Up:Riding the solar system’s race track

Friday

The presentation of the planets visible these September evenings reminds me of a race track.

We earthlings ride one of the race cars on this cosmic track, with eight lanes for the other main entrants.

The Sun of course is in center, and its gravity holds these "cars"- the planets in place. A big difference between the solar system and a car race track is that the planets are not moving under their own power with the driver trying to accelerate and beat the others!

For that reason maybe its better to liken the solar system to a highway rotary- but without anyone changing lanes to reach an exit.

The next clear evening, enjoy the sight of five planets all easily seen with a quick scan of your eyes.

As twilight deepens, look west for the gloriously bright planet Venus, "Race Car #2" from the Sun. Then look under your feet for #3- the Earth. This planet is actually the dimmest at this time, since night has fallen where you are standing and the ones in the night sky are basking in reflected sunlight! Now look in the southwestern sky for "Race Car #5," the bright planet Jupiter.

Turn south and see "Race Car #6," Saturn- not quite as bright as Jupiter.

A short turn left, face southeast for Mars, the ruddy "Race Car #4."

In mid-summer, Venus was higher, and Jupiter, Saturn and Mars were noticeably brighter. Jupiter, Saturn and Mars were also shifted more to the east when night began.

As late summer heads towards fall, we can already notice how Jupiter, Saturn and Mars have shifted westward closer towards Venus, and they have all dimmed.

Now imagine you are a race car driver, speeding along; it’s best not to look behind you of course, but let’s say you catch sight of these other "cars" in your rear view mirror.

Like a flat race track of multiple lanes with cars going one way, the solar system’s main planets orbit roughly on the same level plane, the orbits (lanes) never crossing but staying concentric, and each planet moving in the same direction.

As we on Earth pull ahead, the planets in the outer lanes tend to fall back from our line of sight and our further away. The Earth moves faster than these outer planets (Mars, Jupiter and Saturn) so as we go around the Sun, we eventually will lose them in the glare of the Sun in center.

Venus, on an inner lane, moves faster, and surpasses us.

If you were to watch the outer planets carefully and note their position against the background stars, you will see they will make strange loops, going eastward and then reversing, gimping westward. This is called "retrograde" motion and is an illusion caused by our changing line of sight.

Mercury (#1), Uranus (#7) and Neptune (#8) are also on this "rotary"- or "race track." Mercury, however, is currently visible very low in the east-northeast during morning twilight. Uranus and Neptune rise around 11 p.m. and are a lot dimmer.

The speed of the planets decreases the further from the Sun. Mercury moves at 107,082 miles per hour. Earth travels at 66,615 miles an hour (hold on to your hat!). Neptune moves at 12,146 miles per hour.

This plane of the solar system etched out on the sky forms the ecliptic, where the Sun and Moon also appear to travel. The Sun follows the exact ecliptic while the planets wander anywhere from 7/10 degree to seven degrees above or below the path of the Sun. The Moon’s orbit is inclined 5.1 degrees to the ecliptic.

Most asteroids also follow the ecliptic; Pluto, classified as a "dwarf planet", wanders up to 17 degrees from the ecliptic. Note: a clenched fist held at arm’s length towards the sky spans about 10 degrees.

New Moon is on September 9.

Keep looking up!

— Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at news@neagle.com. Please mention in what newspaper or web site you read this column.

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